The
Light Elements

4
Be

5
B

9
F

15
P

17
Cl

19
K

31
Ga

32
Ge

33
As

34
Se

35
Br

This Java program reads a file containing a list of emission
line wavelengths and their corresponding strengths then simulates
the appearance of the spectrum in a good visual spectroscope.

Hydrogen

Helium

Lithium

Oxygen

Carbon

Nitrogen

Neon

Magnesium

Silicon

Sulfur

Iron

Aluminum

Calcium

Argon

Sodium

Krypton

Xenon

Barium

Strontium

JPEG screen grabs of an applet which computes and plots
the spectra in a web browser window. The above images aren't
dithered. They may appear so if your display doesn't have enough
colors to represent the entire color range. Displays limited to
256 colors or less don't produce acceptable spectra. Try
increasing your color resolution to 16 or 24 bits (16 million
colors).

Note: This program
generates deep 24 bit color plots, therefore you may need to
increase the color depth of your system to view subtle details in
these spectra.

Warning: There may be a
small delay as the Applet loads its element emission line file
and computes the spectra...

Click on an element name in the first column of the table
below to launch the spectra viewer

If you prefer not to run the Applet click corresponding
JPG in the next to last column to obtain an image.

Most common elements in
solar spectrum.(listed in order of decreasing
abundance)

Click on the name in this column to launch the Applet
which displays an emission line spectrum of the
corresponding element

Symbol

Symbol from the table of the elements

Data File

Click on the name to download a text file containing
an a list of emission lines in ┼ngstroms and their
associated strengths for the corresponding element

Emission Lines
4000-7000 ┼

Number of tabulated emission lines in the visible
wavelength range

Jpeg Image

JPEG screen grab (784 X 8). The narrow height is to
reduce transmission time, it expands to 64 pixels using
HEIGHT=64 option in IMG tag of HTML file. To use images
outside the context of a web browser, you should expand
them vertically with image processor.

The element, wavelength range and line width are all
controlled by applet parameter (PARAM) tags in the HTML source
for this page. There are other options such as width and height
of spectra in pixels and contrast which can also be controlled.
There are also options to overlay a continuous blackbody spectrum
of varying strength and to limit the wavelength range.
For example here are the parameters for Neon :

The simulated gas discharge spectrum is synthesized by
assigning each emission line to a gaussian and each point in the
spectra is computed as a mathematical sum of all the emission
lines.

Contrast:

Range: 1 to 10000 (the upper limit comes from
intensity of the weakest line)

Default: 1 (maximum of strongest line assigned to
maximum intensity, no distortion of line profile)

Should be adjusted to 'burn out' the strongest
lines and boost the intensity of the weaker
lines. Should not be too high or some line
blending may occur, also the relative difference
between the various emission line strengths is
lost. A compromise should be reached.

Line Width:

Range: 0 to 100

Default: 3

The width of emission lines is user controlled
and should be adjusted so that the line profile
covers at least one pixel; too small a width
causes undersampling to occur and some lines may
'disappear'! However too broad a line will cause
blending of lines that are closer together.
Again, a compromise must be reached.

Continuum:

Range: 0 to 1

Default: 0.3

Physics: In many plasma environments some
residual broadband background light 'pollutes'
the spectrum, either by scattering from an
external white source or internal transitions
involving the ion continuum. This causes a smooth
background to appear as weak 'rainbow' below the
level of most of the emission lines. This creates
a 'pleasing' colored background which 'fills' in
the empty gap between the emission lines. Here is
an example of the Continuum parameter set to
maximum : Continuum=1 (white
light).

This applet was successfully run under the following browsers
:

NetScape Navigator 3.01

NetScape Communicator 4.01, 4.03, 4.04

HotJava 1.0

Microsoft Internet Explorer v3.01, 4.01

An upcoming version of this Applet will include a more
graphical user interface for controlling these parameters.

This Applet was created by John Talbot. Source code
is available : discharge.java
(Currently limited to 200 emission lines, however this limit can
easily be removed by changing the source code and recompiling.
There are more details on the color
encoding subroutine)

You can also download the source file, class file, these HTML
pages and all the element data as :discharge.zip (76 kBytes)

Physics Background

There are two basic line broadening mechanisms; instrumental
and intrinsic :

Instrumental Broadening

The first is due to finite spectroscopic
resolution and can be controlled by the
researcher. Often higher resolution can be
achieved by larger gratings or coarse gratings
operated in higher order or longer path lengths
for fourier transform spectrometers.

Intrinsic Broadening

The second is fundamental line broadening which
can be caused by at least three factors:

Doppler Broadening

Related to special relativity:
Motion components of a particle
along the line of sight causes a
shift in radiation frequency.
Since particles generally have a
distribution of velocities, this
creates a gaussian blurring in
the spectral lines.

Lifetime Broadening

Quantum mechanical in origin :
Allowed transitions have a short
lifetime and this translates to
some uncertainty in the frequency
of atomic oscillators creating a
Lorentzian line profile.

Density Broadening

Combination of quantum mechanical
and electromagnetic effects: Ions
are bombarded by transient
electric and magnetic fields of
high speed electrons zipping
nearby, these electric fields
split and shift the energy
levels. This constant
perturbation within the plasma
environment depends most strongly
on density and causes strong line
broadening in higher density
plasmas. Temperature, ionization
level and the particular quantum
transition involved also plays a
role.

In most thin plasmas one sees a combination of Doppler and
Lorenztian broadening called Voigt profiles. The Lorentzian
component affects mostly the low intensity 'wings' of the
emission lines so line profiles can be approximated as gaussians,
especially considering the dynamic range limitations of computer
screens. Most of the time spectra taken by researchers do not
fully resolve the intrinsic line profile so the lines are
broadened mainly by instrumental imperfection.

The data for these spectra is courtesy of the Astronomical
Data Center, and the National Space Science Data Center through
the World Data Center A for Rockets and Satellites.